How does it know!

[SC00BY]

How does the human body know things, for example if you pluck your eyebrows the missing one grows back, catches up in length to the other ones and then stops? i assume it stops or we would all be walking around like cousin it! so why does head hair keep growing and eyebrows don't? when they are only inches apart? I guess this could apply to leg hair as well? How does the body know its been pluked/shaved? odd question i know!

[CheekyChops]

I don't know the answer but have always wondered exactly the same myself so am glad you asked!!

Like how do hairs on say your leg, know when they are the correct length and stop growing?  And pubes, they must all grow to a certain length and stop otherwise some people would have pubes that reached to their knees! 

And if you got a leg hair that was say, 5mm long and you cut 2mm off, if would then grow the required 2mm and no more.  How does it know how much you have cut off???

[gen2]

SC00BY,  Hair follicles go through a cycle where they produce hair for x weeks or y months and then shut down for a rest before starting up again.  In humans, the hairs on different parts of our body produce hair for different lengths of time.  The longer they go on producing, the longer the hair becomes, but when the follicle rests, the hair falls out.  This determines the maximum length any hair will grow.

In many animals, the growth / rest periods are synchronised, and the animal goes through a moult.  In humans they are not synchronised and every day some follicles shut down and others start up again.  Hairs on arms and legs have only a short growth period between rests, those in pubic areas grow for longer, and those on our heads may grow for three years or more before taking a rest.  Some animals (eg poodles) have follicles that never take a rest and these need to be constantly clipped to keep them trim.

By the way CheekyChops, hairs are made of dead cells, so neither the hair, nor the follicle know that you have cut 2mm from the end and that hair will always be 2mm shorter than it would have become if it had been left alone.

[Dakota]

WOW Gen, I had wondered the same thing as Scooby and Cheeky, I'm so glad I know now.

[SC00BY]

I am so glad i'm not the only crazy fool to wonder this sort of thing! thanks everyone